Vol.13 No.2 JOURNAL OF TROPICAL METEOROLOGY December 2007

Article ID: 1006-8775(2007) 02-0193-04 ANALYSIS OF TYPHOON MATSA (NO.0509) AFFECTING PROVINCE

1, 2 1 1 1 SUN Xing-chi (孙兴池) , WANG Wen-yi (王文毅) , WANG Ye-hong (王业宏) , GAO Hui-jun (高慧君) , Chen 1 Jin-min (陈金敏)

(1. Shandong Meteorological Observatory, 2. Shandong Institute of Meteorology, Ji’nan 250031 )

Abstract: The characteristics of the moving course of Typhoon Matsa (No.0509), associated heavy rain and physical quantities fields have been analyzed, with the focus on the reason of the typhoon’s abrupt northeastward turn in Province and heavy rain concentrating in the northeast of typhoon center instead of near it. Meaningful conclusions are as follows. The reasons for typhoon abrupt turning are that the subtropical high pressure was moving southward and divergence fields of 200 hPa were to the right of the typhoon center; there was no obvious cold air invading Shandong after the typhoon entered the westerly belt; the southeasterly jet of typhoon and shear brought heavy rainfall to the Shandong peninsula before the typhoon entered Shandong. But after the typhoon’s movement into Shandong, the typhoon’s inverted trough brought the rainfall to the northern and central Shandong.

Key words: Typhoons; affecting Shangdong; track of movement; distribution of severe rainfall CLC number: P458.1.24 Document code: A

1 INTRODUCTION about inflicted serious damage to the coastal area of the province. Areas with rainfall more than 100 mm were China is one of the countries that are severely mainly over the peninsula and northern part and the affected by typhoons. Detailed study has been done on time of heavy rain did not coincide with the eye of the typhoons in the west Pacific with the conclusion that storm. the change of landfall typhoon tracks are subject to the subtropical high, polar fronts and systems of positive 2 DATA AND SCHEME OF NUMERICAL vorticity in the vicinity of the typhoons[1]. Extensive SIMULATION study has been done in the aspect of typhoon activity and abnormal track and associated extreme heavy rain[2 - 7] Conventional weather data and simulations with and a number of research achievements have been the MM5v3.5 were used. Weather maps for 500 and made lately. The 500 hPa vorticity field around the 850 hPa were also used, which give the elements of time influenced by Typhoon No.9711 (Winnie) was [8] geopotential height and wind field. diagnostically analyzed . MM5v3.5 has a good simulation of the process, With a track rarely seen in recent years, Matsa particularly with the rainfall center. For physical made landfall and headed north to affect Shangdong. quantities, the vorticity, diversity, vertical velocity and After moving over land in , it moved northwest divergence of water vapor flux as simulated by the into Anhui and then Bohai Sea after taking passage model in fine mesh were used, which were at the over and Shangdong. It made two turns inside interval of 18 km. The selected domain for the model is Anhui and Shangdong to form a complicated zig-zag shown in Fig.2. track (Fig.1). Matsa was the largest typhoon for Shangdong after 3 ANALYSIS OF TYPHOON TRACK Winnie. The strong wind and heavy rain it brought

Received date: 2006-11-18; revised date: 2007-09-13 Foundation item: National Oceanographic and Meteorological Forecasting and Prewarning System (Phase I) Biography: SUN Xing-chi (1963-), female, native from Shangdong province, senior engineer, mainly undertaking the forecasting of destructive weather of heavy rain and typhoons. E-mail: [email protected]

PDF created with pdfFactory trial version www.pdffactory.com 194 Journal of Tropical Meteorology Vol.13 The post-landfall track of Matsa was complicated, northwest path off the southern rim of the subtropical which moved northwest before turning northward. It is high, with the turning point north of 36°N. In fact, especially noted that quite a number of NWP Matsa suddenly turned toward Jiangsu on Aug.7 for predictions pointed to a westward track when it was two main reasons. still over Anhui in the morning of Aug.7. The eye The key to determine whether the typhoon keep became more difficult to determine as Matsa weakened moving westward or turn north is to know whether rapidly and its central circulation expanded after it there is a well-defined ITCZ south of the subtropical moved inland. Opinions differ among forecasters at high, which is to the east of the typhoon that has made various levels as to where it might be going when it landfall[1]. If yes, the subtropical high will be stationary; suddenly turned to the northeast into Jiangsu. otherwise it will weaken suddenly and move southward. In the case of Matsa, no clear ITCZ was present after it landed in Zhejiang and moved northwest to Anhui. The subtropical high did move southward to expose Matsa on the northern side of the subtropical high, which caused it to shift to Jiangsu from Anhui. One of the important reasons for the typhoon to persist is upper-level divergence. It is known from a comparison of 200 hPa divergence that the storm tended to move with it, which clearly moved toward the northeast of the eye to cause it to turn northeast into Jiangsu. On Aug.7, a high ridge formerly over eastern Siberia moved to northeast China before forming a NW-SE-oriented high ridge. When Matsa was in Shangdong, it was steered by a southeasterly airflow on the southern side of the ridge to move westward again and entered the Bohai Sea.

Fig.1 Track of Matsa and rainfall at 06:00 from Aug. 4 ANALYSIS OF MATSA-INFLICTED 7 to 9. The solid line is for the contour of 50 mm and the shaded area is where rainfall is greater PRECIPITATION than 100 mm. After landfall, heavy precipitation did not coincide with the path of the eye. Before entering Shangdong, the area of heavy rain was to the northeast of Matsa. A N-S inverse trough appeared to its north after it entered the province. A secondary rainfall center appeared in the north of the province, which was in the front of the trough. One of the key points about Matsa was that there were always at the levels below 500 hPa a shear and a cyclonic curvature between the southwesterly and southeasterly to the east of its eye. According to [1], the convergence of wind speed and direction at the circulation center of typhoon, shears in different portions of its lower levels and cyclonically curved streamlines within the inflow layer all contribute to the generation and strengthening of conditions under which convergence occurs and the rainfall center of the typhoon often coincides with these characteristics. The Fig.2 Simulated domain for dual nested meshes. shear and cyclonic curvature east of the storm dislocated the center of heavy rain to the east. On Aug.5, Matsa was about to land in a pattern Matsa shows asymmetric structure. It is known that looked like it would be going north after landfall. from the visible cloud imagery and 500 hPa pattern The ridge line of the subtropical high at 120°E was after landfall that it had an extensive, trailing cloud north of 36°N, indicating that it would continue its system, which was associated with the presence of the

PDF crea194ted with pdfFactory trial version www.pdffactory.com No.2 SUN Xing-chi (孙兴池) and WANG Wen-yi (王文毅) et al. 195 shear. for the generation of heavy rain. The 200 hPa Usually, the strong wind around the typhoon is divergence had two centers in both the northern and evenly distributed around the eye. The interaction southern parts of the peninsula, corresponding to two between the subtropical high and westerly system will centers of heavy rain in Yantai / Weihai and Qingdao. change it into asymmetric distribution, which then A main 200 hPa divergence area moved to the leads to asymmetric distribution of vorticity. and Bohai Sea in the morning of Aug.8, As shown in the pattern of 500 hPa for Aug.7, there were two divergence centers in the central and winds stronger than 12 m/s around the eye was evenly northern Yellow Sea and divergence was clearly seen distributed across all quadrants of the typhoon in northeastern peninsula and northern Shangdong. In circulation. The 500 hPa vorticity was centered around the latter area, precipitation began to intensify in the the typhoon and so was the center of positive vorticity. morning of Aug.8 and heavy rain occurred in the Late on that day, a southeasterly jet stream occurred afternoon. It is then seen that upper-level divergence between the area east of the storm and the subtropical was always on the northern side of the eye, which was high when wind speed became smaller southwest of the one of the reasons why the heavy rain area was on the typhoon to increase the positive vorticity north of it. northern side of the eye. From the night of Aug.7 to the early morning of Aug.8, It is known from the vertical, zonal distribution of heavy rain occurred in the southeastern part of the divergence around the eye for the night of Aug.7 that province. In the morning of Aug.8, Matsa was around airflow converged beneath 600 hPa and quite strongly Linyi when the positive 500 hPa vorticity was over the between 900 hPa and 650 hPa, suggesting that the northern part of Shangdong Peninsula and there was a latter be the maximum inflow layer of warm and humid center of positive vorticity over the Straight of Bohai airflow in lower levels. Airflow diverged above 600 Sea. The 6-h rainfall was more than 50 mm from 02:00 hPa, with the maximum between 500 hPa and 400 hPa. to 08:00 on Aug.8 in northeastern Shangdong Divergence was quite intense at 200 hPa. The inflow of Peninsula, with the maximum at 99 mm. In the low-level mass was in equilibrium with the outflow of afternoon, positive vorticity covered northern upper-level mass. Compared to a previous statistical Shangdong so that heavy rain, even unusually heavy work[10], the upper-level outflow was very strong in this rain, occurred during the day in this part of the case. province, which concentrated at 08:00 through 20:00. With Matsa in Shangdong, the easterly north of the The abundance of water vapor and its continuous typhoon climbed over hills and low-lying mountains in supply to the typhoon system are two basic conditions Jiaodong and central and southern parts of the province for the typhoon-induced heavy rain to persist. Low- before descending and expanding over the plain in the level jet stream is the key to moisture transportation. northwestern part. Consequently, positive vorticity From the analysis of the 850 hPa situation, it is known increased, strong northeasterly wind appeared in that a low-level jet stream stronger than 16 m/s was northern Shangdong and the inverse trough north of extending from northern Jiangsu to the peninsula part Matsa strengthened. At the time, the 500 hPa inverse of Shangdong, in front of which laid a well-defined S to trough of the typhoon was more westward than the 850 SE shear. Corresponding to it, water vapor converged hPa one, i.e., the trough line slanted westward with over the northeastern part of the peninsula and northern altitude in the troposphere. It made it possible for warm Shangdong, with the center over Yantai and Weihai. and humid air stream to be transported by the The divergence of water vapor was also large in southeasterly from the rear of the trough to the front of northwestern Shangdong, contributing to another center it and significant convergence of water vapor flux of heavy rain. Water vapor was in divergence in occurred in both the front and rear of the inverse trough. southern and southeastern parts of the province, As a result, heavy rain also took place in northern resulting in less rainfall in these regions. Shangdong, even though it was in front of it. Water vapor and ascending motion are the two For analyses of other aspects, refer to the Chinese most basic conditions for typhoon-induced precipitation. edition of the journal. From the 500 hPa vertical velocity from the night of Aug.7 to the morning of Aug.8, it is known that the 5 SUMMARY maximum ascending velocity gained the order of magnitude for mesoscale ascending velocity[9], which (1) Changes in the subtropical high and high was much higher than the index for regional heavy rain pressure within the westerly zone are vital for the in Shangdong[10]. typhoon track and special attention should be paid to Upper-level divergence maintains the ascending the possibility that the subtropical high may suddenly motion in the middle and lower levels of the retreat eastward and southward after landfall. troposphere, which is one of the important conditions (2) The 200 hPa divergence field is indicative of

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